1. Field of the Invention
The subject matter of the present invention is a process for disinfecting hot tap water in hot water supply systems of buildings. The process serves in particular to kill heat-stable bacteria which develop in water at temperatures between 40.degree. and 60.degree. C. The process is especially useful for disinfection of hot water pipes in hospitals.
2. Related Art
Since the first appearance of the so-called legionnaires' disease in 1976, it is known that the pathogen which causes this disease, legionella pneumophila, is not uncommon and is very widespread in nature. It has been shown that temperatures of up to 45.degree. C. are favorable for the development of this pathogen. Since temperatures of around 50.degree. C. in hot water supply systems do not suffice to kill these microorganisms, water in hot water supply systems is heated, as a rule, to higher temperatures. This fact entails energy costs for hospitals which are not insignificant, and moreover promotes deposits in piping.
The internally transmissible legionnaire's pneumonia has become a serious problem in hospitals. While legionella are unable to cause illness in most healthy human beings, they lead to the outbreak of disease in the sick and the infirm. Since this problem is well known, various methods have been proposed to kill these bacteria in the hot water distribution systems in hospitals. Proposed as methods have been hyperchlorination, thermal treatment, ozonization, UV treatment and the addition of metal ions such as copper and silver ions. The simplest method so far has been thermal treatment of the water. This has the disadvantage, however, that energy costs for water conditioning are higher and that water comes out of the taps at very high temperatures. Hyperchlorination has the main disadvantage that the pipes are thereby corroded and that carcinogenic by-products may be produced. With UV treatment, problems arise if calcareous deposits are formed on the UV source, diminishing the efficiency of the treatment. Contact with water can also damage the lamps. In the case of treatment with metal ions, the main disadvantage is that the water has to be mixed with chemical substances which then remain in the water. This can lead to undesired reactions in the user and to the accumulation of heavy metal ions in waste water.
Ozone treatment has the advantage that only a short contact with the bacteria or the virus is necessary in order to kill it. It can be learned from scientific literature that a dose of 1 to 2 mg/liter of ozone is expedient for the treatment of tap water. Since ozone decomposes relatively quickly, and since, on the other hand, ozone has undesirable characteristics when in high concentrations, it is necessary that the dose of ozone be adapted precisely to the water distribution system. On the one hand, the ozone concentration must lie below that which could have a harmful effect on the water user. On the other hand, the ozone concentration must be sufficient to kill the harmful organisms in the water. Owing to the characteristics of ozone, its use for the disinfection of hot water supply systems until now has entailed problems which have limited its application.